1. Field of the Invention
The present invention relates to oxygen sensors used in association with the internal combustion engine of motor vehicles, and more particularly for a method of adjustment thereto.
2. Description of the Prior Art
Oxygen sensors are used in virtually all currently produced gasoline internal combustion engines used for vehicles operated in the United States. As shown diagrammatically at FIG. 1, the oxygen sensor 10 is located at exhaust pipe 12 so as to be in communication with the exhaust gas 14 therein in order to sense the oxygen content thereof, and provide an output signal voltage 16 responsive thereto. This oxygen sensor output signal voltage 16 is input, along with other sensor signals, to the engine computer control module (CCM) 18, which then, based upon predetermined criteria, provides one or more signals 20 to various components associated with the engine 22, particularly the fuel injector 25, to optimally adjust operational parameters thereof to provide performance yet minimize both fuel consumption and exhaust gas pollution.
As shown at FIGS. 2 and 3, the oxygen sensor 10 is a device consisting of a zirconia ceramic sensor element tip 24 for producing the output signal voltage 16 (see FIG. 1), wherein the sensor element tip is mounted to a housing 26 and protected by a perforated cover 28, whereby the perforations 40 allow the exhaust gas to contact the sensing element tip. The oxygen sensor 10 has threads 30 for being threadably mounted to a mounting member 32 via a hex 36. The mounting member 32 is, in turn, welded 34 to the exhaust pipe 12. The housing 26 and the weld 34 prevent exhaust gas from escaping the exhaust pipe 12 thereat. An output signal wire 38 is connected to the sensor element tip 24, emanates from the housing 26, and is connected (typically) to the engine CCM 18 (see FIG. 1).
The technique to locate an oxygen sensor in the exhaust pipe has not changed over the last twenty-five years: the housing 26 of the oxygen sensor 10 is screwed into the mounting member 32, whereby the sensing element tip 24 extends outwardly a distance d equal to about fifteen millimeters. This technique while simple and repeatable, is not always optimal. The reason for this is that for the oxygen sensor is most accurate when operated within a specific temperature range set by the manufacturer. While heaters may provide a temperature at or above a low-side value of the specific temperature range for the oxygen sensor when the exhaust gas is cold (i.e., a cold engine start), there is no reasonable way to cool the temperature of the oxygen sensor to an allowable high-side value of the specific temperature range when the temperature of the exhaust gas exceeds this value. This later case may occur, for example, when the vehicle is towing and traveling upgrade, and heavy trucks are most prone to experiencing this behavior.
One way to limit higher end operational temperature of the oxygen sensor may be to place the oxygen sensor further downstream along the exhaust pipe. But, in practice, the excessive distance needed for a noticeable drop in exhaust gas temperature (as for example fifteen feet) renders this an impractical solution. Another solution may be to make the outward extension distance d smaller, on the theory that the reduced contact surface area will result in less heat exchanged with the exhaust gasses and the heat transfer rate away from the sensor element tip will be the same or improved (because of the shortened heat conduction path to the exhaust pipe sidewall). However, in practice the extension distance d may become too small, such that insufficient exposure to the exhaust gas can occur, resulting in less accurate output signal voltages.
Accordingly, what remains needed in the art is some method whereby the oxygen sensor may be installed and operate within the temperature limits set by the manufacturer under all operating conditions of the vehicle.